COLUMBIA, Mo. - Dixie had a problem. The 17-year-old Tennessee Walker horse had received numerous unsuccessful treatments for a tumor on her eyelid. The tumor was damaging her eyelid, and without the lid, the horse's eye would not survive. With no universal form of treatment, a University of Missouri-Columbia veterinarian decided to use a method commonly used in human medicine, and within a few weeks, Dixie's eye had returned to normal and was healthy.

Dixie had squamous cell carcinoma, one of the most common cancers of the eye. The tumor is classified as perioccular because it affects the eye and surrounding tissue including the eyelid. It is extremely difficult to perform any type of skin graft on a horse's face. As a result, if a horse's eyelid is removed, the eye also must be removed in most cases. Elizabeth Giuliano, an assistant professor of veterinary medicine and surgery, used a common human therapy called photodynamic therapy to kill the tumor and save Dixie's vision.

To use photodynamic therapy, surgeons first inject a drug into the body and wait 24 to 48 hours for the drug to circulate in the body and attach and accumulate in the tumor. Depending on the drug used, the surgeon matches a specific laser that will activate the drug. When the drug is activated, it creates oxygen free radicals that destroy the tumor. Giuliano uses a novel approach with photodynamic therapy. She injects the drug directly into the tumor bed and then treats the animals with the laser light. Since her treatment, Dixie's prognosis for long-term recovery is excellent as she recovered the use of her eye.

"While we were the first ones to use this therapy in this way in horses, we do still have many questions to answer," Giuliano said. "The method appears to be extremely effective and very safe. It also appears to require fewer stays in the hospital than other treatments. We do know that the horse may experience some sensitivity to light for a short period of time, but long-term recovery appears to be excellent."

To date, Giuliano has treated five horses and seen similar improvement in all of them. All the horses are white or light in skin color, which is typical for this type of cancer, as lightly pigmented horses are more at risk, Giuliano said. Currently, she is looking for additional horses with this specific type of eye cancer to study the treatment further.

Giuliano recently presented her preliminary results to the American College of Veterinary Ophthalmologists. The Morris Animal Foundation is funding the work.